Workout streak banner: swipeable week / year / vs-last-week pages

Replaces the single lifetime-tally banner (which used a meaningless streak%7
tick bar) with a 3-page paged TabView:
  1. This week — count + 7 per-day ticks for the current week
  2. This year — count + 12 month ticks, with all-time total underneath
  3. vs last week — this week's count and the delta (▲ more / ▼ fewer / same)

Adds WorkoutViewModel breakdowns: workoutsThisWeek/LastWeek/ThisYear,
currentWeekDays (7 flags), currentYearMonths (12 flags).

(Not build-verified — sim runtime removed to reclaim disk; uses only APIs
already present in the original banner.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCal/Models/ExerciseModels.swift

@@ -262,6 +262,58 @@ class WorkoutViewModel: ObservableObject {
         Set(workoutDates).count
     }
 
+    // MARK: - Streak-banner breakdowns (this week / this year / comparison)
+
+    /// Workout days in the week `offset` weeks from now (0 = current, -1 = last).
+    private func workoutCount(inWeekOffset offset: Int) -> Int {
+        let cal = Calendar.current
+        guard let ref = cal.date(byAdding: .weekOfYear, value: offset, to: Date()),
+              let wk = cal.dateInterval(of: .weekOfYear, for: ref) else { return 0 }
+        let set = Set(workoutDates)
+        return (0..<7).reduce(0) { acc, i in
+            guard let d = cal.date(byAdding: .day, value: i, to: wk.start) else { return acc }
+            return acc + (set.contains(iso.string(from: d)) ? 1 : 0)
+        }
+    }
+
+    var workoutsThisWeek: Int { workoutCount(inWeekOffset: 0) }
+    var workoutsLastWeek: Int { workoutCount(inWeekOffset: -1) }
+
+    var workoutsThisYear: Int {
+        let cal = Calendar.current
+        let year = cal.component(.year, from: Date())
+        return Set(workoutDates).filter {
+            guard let d = iso.date(from: $0) else { return false }
+            return cal.component(.year, from: d) == year
+        }.count
+    }
+
+    /// 7 flags for the current week (calendar week order) — true if worked out that day.
+    var currentWeekDays: [Bool] {
+        let cal = Calendar.current
+        guard let wk = cal.dateInterval(of: .weekOfYear, for: Date()) else {
+            return Array(repeating: false, count: 7)
+        }
+        let set = Set(workoutDates)
+        return (0..<7).map { i in
+            guard let d = cal.date(byAdding: .day, value: i, to: wk.start) else { return false }
+            return set.contains(iso.string(from: d))
+        }
+    }
+
+    /// 12 flags for the current year — true if ≥1 workout that month.
+    var currentYearMonths: [Bool] {
+        let cal = Calendar.current
+        let year = cal.component(.year, from: Date())
+        var months = Array(repeating: false, count: 12)
+        for s in workoutDates {
+            guard let d = iso.date(from: s), cal.component(.year, from: d) == year else { continue }
+            let m = cal.component(.month, from: d) - 1
+            if (0..<12).contains(m) { months[m] = true }
+        }
+        return months
+    }
+
     private let iso: DateFormatter = {
         let f = DateFormatter(); f.dateFormat = "yyyy-MM-dd"; return f
     }()